The present invention relates to a hard disk drive used as a data storage medium, and more particularly to a hard disk drive, an optimization process of which is individually executed, for example, when the drive is manufactured.
A hard disk drive (HDD) broadly used as a data storage medium for computers, and the like, comprises a magnetic head that reads user data stored on a magnetic disk or writes user data to the magnetic disk. The magnetic head is mounted to an actuator moved by a VCM (Voice Coil Motor). When the magnetic head reads/writes user data, the actuator is driven to move and position the magnetic head at a specific track. Movement of the magnetic head to a given location is controlled according to servo information stored on the magnetic disk.
On a magnetic disk such as a hard disk, a plurality of data tracks are formed in the shape of concentric circles, and servo tracks where identification data and a burst pattern are stored beforehand are formed in a radial direction on the magnetic disk. The above-mentioned servo information includes the identification data and the burst pattern. The identification data information indicates a track address for each data track. On the basis of the identification data read by the read head, a read head and a write head can judge the position of a data track. In addition, the burst pattern is composed of a plurality of burst pattern lines in which signal-stored areas are arranged at constant intervals in a radial direction on the magnetic disk, and the phases of the signal-stored areas are different from one another. According to a signal (Position Error Signal: PES) that is output from the read head in response to the burst pattern, it is possible to detect deviation, i.e., how much a position of the read head or write head deviates from a target data track.
This servo information is written to the magnetic disk in the manufacturing process before shipping the hard disk drive as a product. In order to correctly read or write user data, it is necessary to write reference servo information with accuracy. In recent years, the self-servo write (SSW) method performed by a hard disk drive itself has been proposed and has also been put into practical use, as discussed in Japanese Patent Laid-open No. 11-45405 (pages 9-10) and Japanese Patent Laid-open No. 2002-8331 (page 3).
Unlike conventional electrical machinery and apparatuses, a hard disk drive is provided with a large amount of data, such as how to write the servo information. When manufacturing the hard disk drive, a long time is spent in executing the optimization/inspection process of the newly assembled hard disk drive. This optimization/inspection process includes, for example, the following processes:
(1) a writing process for servo information;
(2) a pretest process to optimize coefficients of various kinds of servo systems and channel systems; and
(3) a function/reliability verification test process on the basis of a long-run test.
However, because each of the processes requires a dedicated inspection apparatus, the investment in inspection apparatuses becomes huge when manufacturing a large amount of hard disk drives. Accordingly, the investment in inspection apparatuses increases the cost impact, which also exerts a direct influence on the decision regarding scale of production. Moreover, in a case where the self-servo-write method described in the above-mentioned Japanese patent documents is adopted, the necessity of the inspection apparatuses arises in like manner.